The enormous clinical promise of stem cells makes these cells prime candidates to investigate their potential for the restoration of inner ear damage. Inner ear progenitor cells have recently been generated from adult murine inner ear stem cells and it has been shown that these progenitor cells can give rise to hair cells and neurons in vitro. Transplantation of murine inner ear progenitor cells into the developing inner ear resulted in the generation of hair cells in vivo. In pilot experiments using adult human inner ear tissue samples obtained in labyrinthectomy surgery, we found evidence for the presence of adult stem cells in the human inner ear. In vitro, these stem cells could be propagated and differentiated into cells that express marker proteins indicative of hair cells. This preliminary evidence suggests that human hair cells can be generated from adult human inner ear stem cells. The research proposed in this Feasibility Pilot Study focuses on establishing the most seminal requirements for the utilization of human adult inner ear stem cells in future research and in clinical applications. In Aim 1, we will characterize the potential of human inner ear stem cells to give rise to inner ear progenitor cells that can differentiate into hair cells. In Aim 2, we will investigate the long-term propagation capacities of human adult stem cells. Here we plan to develop a method that allows us to expand the stem cell population with the goal of establishing long-term storage of human inner ear stem cells in liquid nitrogen. Expansion and long-term storage are the principal requirements for further research on human adult inner ear stem cells and, potentially, for the future development of an inner ear stem cell donor bank. Subsequent research aimed to translate stem cell technology toward human therapy will only be possible by first establishing reliable and efficient methodology to isolate, expand, propagate, and store human inner ear stem cells, the goals proposed in this Exploratory Research Grant application. [unreadable] [unreadable]